CARLSBAD  For one week, La Costa Resort and Spa was CoCo Vandeweghe’s realm. On its courts she performed with a certainty that marked her as a tennis player of the highest promise.

One year later, Vandeweghe is preparing to return to La Costa for the Mercury Insurance Open Presented by Tri-City Medical Center, beginning July 30. She remains, with her height and her power, a player of potential, but now there are questions.

The Carlsbad resident has to establish that she can achieve consistency, which to now has escaped her. “I would have loved my first year to make a huge splash,” she said Friday during a news conference, “but I definitely didn’t realize all the different levels there are of playing on the WTA Tour.”

For the Mercury, Vandeweghe has been awarded a wild card into the main draw, which she did not have in 2010 when she had to battle through qualifying to reach the main event. Once in it, she outplayed Vera Zvonareva in the second round and was not stopped until Svetlana Kuznetsova, later the tournament champion, got past her in the quarterfinals.

“It kind of catapulted me to where my ranking is today,” Vandeweghe said.

Before that week, Vandeweghe was ranked No. 205, according to Vani Vosburgh, manager of communications and statistics for the tour. By week’s end, she had advanced to No. 168.

A player, however, retains the points accrued in a particular event for only a year. The awards Vandeweghe won at La Costa in 2010 come off for this year’s Mercury event. Unless she at least repeats making the quarters, her ranking, currently No. 99, is going to spiral higher.

On neither clay nor grass courts has Vandeweghe displayed much efficiency. Raquel Giscafre, the Mercury’s tournament director, said the San Diego County woman might be wise to seek the counsel of Conchita Martinez, who knew her way around clay courts. Martinez has a home here.

Accepting that she should fit as many matches as possible into her schedule after the end of the clay court season, Vandeweghe has been playing World Team Tennis for the Boston Lobsters. Among her opponents: Serena Williams.

Tied at 4-4, one match came down to a super tiebreaker. The winner of the next point would win the match. Vandeweghe was to serve. She said she was advised to go to a kick serve and play a serve-and-volley point.

“Are you crazy?” Vandeweghe said she responded. “I just couldn’t do it.”

Vandeweghe did go to the net. “She passed me cross-court,” she said of Serena.

Vandeweghe is the granddaughter of Ernie Vandeweghe, who played seven seasons in the 1950s with the New York Knicks. The senior Vandeweghe, 82, recently had a suggestion for CoCo — that she resume an association with Guy Fritz, once the tennis pro next door for the Vandeweghes. Fritz began working with CoCo when she was 10.

Ernie Vandeweghe remembered that under Fritz, CoCo had her serve caught at 120 mph.

“She was considerably over that,” said Fritz. By his account, Vandeweghe has not reached 115 in the past two years.

“They just asked me to come in and work on her serve a little bit,” Fritz said. He was talking about a tennis player who has not fulfilled her promise.